It would appear that the Clarion unit runs on the C-Bus system. At least that was the protocol that Clarion were using when the P38 was being made.
If ours are C-Bus then....
Pin 6 = Signal Ground
Pin7 = CD L Ch Input
Pin 8 - CD R Ch Input.
There is a picture of the C-Bus pinouts here...
Search Results clarion » Mictronics
I found this from a Saab forum earlier, a guy has done a similar mod, and I'm just copying and pasting.....
"We are only concerned with pins 5,6,7,8 and 9.
This is what i did.
I bought a small box, a male 13 pin DIN connector (has 3 rows of 4 pins and 1 at the bottom as the 4th row,) some 6 core cable (you only need 5 core) an rca input mount (for left and right) and a switch. (I also bought a cable gland to stop any unwanted tugging on the cabel pulling out the solder joints)
Simply connect the switch across pins 5 and 9. (Upon closing the switch while the unit is running, it will automatically enter slave mode thinking a CD changer magazine has just become active, and therefore accept audio inputs from the CBUS socket instead)
Next connect your RIGHT auido RCA to PIN 8.
Connect your LEFT audio RCA to PIN 7
Connect GND of both RCA sockets together, and then solder this wire to PIN 6.
Seal up your box and plug in. Plug in your ipod, turn the ignition and flick the switch, the unit will enter (accs) mode on the screen, and you'll hear your music loud and crystal clear thru your factory setup."
Could be a good place to start. Especially if switching pin 5 and 9 causes the HU to switch to accessory mode and just amplify whatever is coming down pins 7 and 8. The only other thing I'd like to have would be a way of connecting up to the power and dropping the voltage to 5.5v so you can charge the ipod too.